Structural effects of C3 oxygenated fuels on soot formation in ethylene coflow diffusion flames

This paper investigates how the structure of three C3 oxygenated fuels: dimethyl carbonate (DMC), dimethoxymethane (DMM) and isopropanol (IPA) influences soot formation when the fuels are blended with ethylene in laminar coflow diffusion flames. Up to 20% of the total carbon was substituted with oxygenated fuel. Colour-ratio pyrometry was used to measure the soot volume fraction (f(v)). IPA caused a strong increase in f(v), whereas DMM and DMC both caused an initial increase followed by a progres-sive decrease in f(v) as the proportion of oxygenated fuel was increased. Differential mobility spectrometry and thermocouple probes were used to measure the particle size distribution and gas temperature in the flames at 5% blend strength. The hottest region of the 5% flames was consistently about 100 K cooler than the corresponding region of the ethylene flame, indicating a thermal effect of the doping. The 5% flames showed an increase in the maximum centre-line average particle size and fv versus the ethylene flame, with the IPA showing the largest increase. The evolution of the centre-line particle size distribu-tions showed that the 5% flames experienced earlier particle growth compared to the ethylene flame. Consideration of the role of the chemical pathways towards benzene formation suggests that methyl rad-icals from the decomposition of the oxygenated fuels are responsible for the increase in f(v) at 5% doping. The difference in f(v) between the IPA versus DMM and DMC flames is thought to be due to the addi-tional presence of C3 species originating from the carbon-carbon bonded backbone of IPA. Meanwhile, the differences between the DMC versus DMM flames are thought to arise from CO2 produced during the decomposition of DMC, and a corresponding thermal effect where the pyrolysis region of the 5% DMC flame was observed to be about 50 K cooler than the other flames. (C) 2021 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

This study investigates the impact of the structure of three C3 oxygenated fuels on soot formation in laminar coflow diffusion flames when blended with ethylene. It was found that different oxygenated fuels have different effects on the soot volume fraction (f(v)), with IPA causing a significant increase, while DMM and DMC showed initial increases followed by decreases in f(v) as the proportion of oxygenated fuel increased.